Effect of pH, silicon and phosphorus treatments on growth and yield of papaya (Carica papaya L.)

Adlan, Hassan Ali
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Field and laboratory experiments to evaluate pH, silicon and phosphorus effects on papaya were conducted on the island of Kauai on an aluminous ferruginous latosol. The main plots were soil pH (5, 6 and 7) attained by liming, subplots were Si levels 0, 833 and 1166 kg per ha and three P levels, 0, 560 and 1120 kg per ha were superimposed on the Si subplots in a 3x3x3 factorial with three replications. With addition of P there was a highly significant (P=0.01) increase in plant height with age. Growth was suppressed in zero-P treatments, culminating in death of the plants. Silicon treatment produced a very limited growth response. At pH 7 plant growth increased significantly (P=0.05) . In general growth was highly influenced by the relative sufficiencies of lime and P. Although analysis of variance indicated no significant effect due to Si application, multiple regression equations revealed a positive effect of Si at later stages of growth. Papaya fruit yields, both total and total marketable, increased significantly (P=0.01) with P treatment, and with pH levels (P=0.01). A trend for increased yield with Si treatment was not statistically significant. Monthly yield increased under all levels of treatment. Trees in the zero-P treatment produced almost no fruit. Fruit quality, as determined by pH of fruit juice, titrateable acidity, Brix percentage and Brix-acid ratio, did not differ with treatment. A Brix percentage of 11.5 is tentatively suggested as a measure of fruit maturity in papaya. Plant and soil analyses related closely to growth effects. With increased P, P concentrations increased in petioles and blades. In zero-P treatments, P concentrations remained almost constant throughout the soil pH range. Intermediate levels of Si increased plant P, but these values decreased with highest Si application. Multiple regression equations revealed a close relationship between P, Si and Ca in the plant. The petiole was more sensitive to Si treatment than the blade. Silicon concentrations in both petioles and blades increased with increasing pH and P applied. Whole plant samples at flowering indicated similar patterns of nutrient accumulation in the stem and petiole. Phosphorus, Si and Ca increased in all tissues with increasing treatments. Dry weight of whole plants increased with increased treatment levels. Increasing P caused a marked decrease in the number of days to flowering. Total nutrient uptake at flowering by the papaya was calculated in kg per ha. Nutrient uptake increased with increasing treatment and with higher pH. Calcium increased in both blades and petioles with age. Generally Ca was higher in the blade than the petiole. There was a trend of increased Ca concentration with increased P applied especially at high pH. Leaf Ca also increased with increasing pH. Exchangeable soil Ca values increased with higher pH. Extractable soil Si increased with Si treatment; within one Si treatment extractable soil Si increased with higher P applied. Silicon increased from pH 5 to pH 6 and then decreased from pH 6 to pH 7. In zero-P treatments soil Si remained constant throughout the whole range of sampling intervals. There was a tendency for extractable Si to decrease with time. Silicon application did not affect the native soil P, but with increasing P treatment, Si seemed to cause an increase in extractable soil P. A relationship was established between incidence of Phytophthora parasitica blight of papaya and pH 6, in that maximum spread of the blight occurred at pH 6.
Thesis (Ph. D.)--University of Hawaii, 1969.
Bibliography: leaves 183-204.
xi, 204 l illus
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Theses for the degree of Doctor of Philosophy (University of Hawaii (Honolulu)). Agronomy and Soil Science; no. 225
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